Although hard disk can be seen everywhere in our life, not everyone knows its storage mode and principle.
Imagine a plane flying at a height of 1 mm above the ground, circling the earth once every 25 seconds, covering every inch of the surface.
Reduce it to the size of the palm of your hand and you will get something similar to a modern hard disk, which contains more information than your local library.
So how does it store so much information in such a small space?
There are a large number of high-speed rotating disks in the center of each hard disk, and the surface of each disk has a recording head that sweeps at high speed.
Each disk is covered with a thin and tiny layer of magnetized metal particles, and the data exists in a form that cannot be distinguished by the naked eye.
Magnetization patterns formed by many groups of tiny particles are recorded to form data.
Each group, also called bits, all particles are arranged according to their own magnetism, forming one of two states, corresponding to 0 or 1.
By converting bit information into current through electromagnet, data can be read and written on the hard disk.
This magnet will produce a strong magnetic field, which is enough to change the magnetism of metal particles.
When information is written to the disk, the drive uses a magnetic reader to restore it to a meaningful form, similar to the phonograph needle converting record lines into music.
But how did you get so much information from 0 and 1?
In fact, it is a lot of combinations of 0 and 1.
For example, a byte, that is, 8 bits can represent a letter. On average, each photo has several megabytes, and each megabit is equivalent to 8 million bits.
Because every bit must be written on the physical surface of the disk, we have been looking for ways to increase the magnetic recording density of the disk, or to increase the number of bits that can be accommodated per square centimeter.
The magnetic recording density of modern hard disk is about 93 gigabits per square centimeter, which is 300 million times that of IBM's first hard disk in 1957.
The huge increase in storage capacity is not only due to shrinking everything, but also includes many innovative technologies.
A technique called thin film lithography enables engineers to shrink readers.
In addition to size, readers can become more sensitive by making use of new discoveries in the magnetic and quantum properties of matter.
The appearance of mathematical algorithm can make the bit arrangement more compact, filter the noise caused by electromagnetic interference, and find the most possible bit order from a large number of read-back information.
The thermal expansion of the magnetic head is controlled by placing a heater under the magnetic recorder, so that it can be suspended within 5 nanometers of the disk surface, which is about the width of two DNA chains.
In the past few decades, the storage capacity and performance of computers have been greatly improved according to a model called Moore's Law, which predicts that the information density will double every two years in 1975.
However, if it exceeds 15.5 gigabits per square centimeter, the magnetic particles will continue to shrink or be plugged more tightly, and the "superparamagnetic effect" will occur.
That is, when the volume of magnetic particles is too small, their magnetism is easily disturbed by thermal energy, which leads to bit orientation confusion and data loss.
Scientists solved the problem in a very simple way:
Changing the magnetic recording direction from horizontal to vertical increases the magnetic recording density to nearly 0. 155 terabytes per square centimeter (1000 gigabytes).
Recently, the magnetic recording density has been improved by heat-assisted magnetic recording technology.
This technology uses a thermally stable recording medium to temporarily reduce the magnetoresistance by local laser heating, thus realizing data writing.
Although these drive disks are still in the prototype stage, scientists have played a new trick: bit-regular media.
The corresponding positions of bits are arranged in independent nano-scale structures, which potentially achieves a magnetic recording density of 3. 1 terabyte per square centimeter, or even more.
Thanks to the joint efforts of several generations of engineers, materials scientists and quantum physicists, this incredibly powerful and extremely accurate gadget can rotate in the palm of your hand.
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